1. Technical Field
The present invention relates to a fluorobicyclo[2.2.2]octane compound which is useful typically as a liquid crystal material adoptable to liquid crystal elements, a method of producing the same, and applications thereof.
2. Background Art
In recent years, display elements using liquid-crystalline compounds (liquid crystal display elements) have extensively been expanding their ranges of application. The liquid crystal display elements use optical (refractive index) anisotropy (Δn) and dielectric anisotropy (Δ∈), which are characteristics specific to liquid crystal compounds, and are applied to watch, calculator, various measuring instruments, automotive panel, word processor, electronic organizer, mobile phone, printer, computer, television set, and so forth.
The liquid crystal compounds show specific liquid crystal phases characterized between solid phase and liquid phase, and the liquid crystal phases may roughly be classified into nematic phase, smectic phase, and cholesteric phase. Among them, the nematic phase has most widely been adopted as the phase of liquid crystal for display elements, or so-called liquid crystal to be driven. Display modes of the liquid crystal display elements actually proposed at present include dynamic scattering (DS) type, guest-host (GH) type, twisted nematic (TN) type, super-twisted nematic (STN) type, thin-film transistor (TFT) type, and ferroelectric liquid crystal (FLC) type. Known driving systems include static driving system, time-division driving system, active-matrix driving system, and dual-frequency driving system.
The TN-mode liquid crystal display element is disadvantageous due to its low response speed and poor viewing-angle characteristics when it is used under the active-matrix driving system widely adopted at present, and remains problematic for applications such as TV, where the viewing-angle characteristics are highly appreciated. In contrast, the VA (vertical alignment) mode and the IPS (in-plane switching) mode are known to be advantageous in terms of wide viewing angle, short response time, high contrast and so forth. The VA mode is a mode most widely adopted to large-sized television set at present. Liquid crystal composition used for the VA type liquid crystal display element adopted herein is required to have large negative dielectric anisotropy, wide temperature range allowing the nematic phase expressed therein, and high chemical stability. As an example of the compound having negative dielectric anisotropy, German Patent No. DE3906058 describes a compound having a 2,3-difluorophenyl group. Recent trends in elevation in the driving frequency of the liquid crystal display device up to 120 Hz or above have raised the need for a liquid crystal material capable of rapidly responding to applied voltage. None of the conventional liquid crystal materials, however, have sufficiently large levels of dielectric anisotropy Δ∈ necessary for rapid response, so that it has therefore been expected to develop a liquid crystal material having a larger negative dielectric anisotropy Δ∈.
In order to increase the negative level of the dielectric anisotropy Δ∈ of a rod-like organic compound, it is generally effective to design the molecule so as to have a dipole moment in the direction orthogonal to the longitudinal direction thereof. More specifically, a method widely adopted is such as substituting the molecule with a cyano group, or halogen atom, so as to express the dipole moment in the direction orthogonal to the longitudinal direction.
A large number of liquid crystal compounds having benzene rings substituted with fluorine atoms, such as those disclosed in German Patent No. DE3906058 have been known, but there are only a few reports on compounds having a ring structure other than benzene ring, wherein the ring structure is partially substituted. In particular, no compound having a bicyclo[2.2.2]octane skeleton, having its hydrogen atoms at the 2- and 3-positions with three or more fluorine atoms has been known.